1. Field of The Invention
The present invention relates to improvements in powered, hand-held apparatus of the type having a pair of reciprocating cutting members, for trimming hedges, shrubs, and the like.
2. Description of The Prior Art
Hand-held trimming devices of the type described above are well known in the gardening tool art. Such devices are conventionally electrically powered and can be equipped with a cord extension for accepting externally provided power or can be completely self-contained, having a rechargeable battery pack. A schematic diagram of a conventional electrically powered hand-held trimmer appears in FIG. 1 and is designated generally by the numeral 1.
Essentially, trimmer 1 has a stationary elongated member 2 with a plurality of slots 3 disposed generally perpendicular to the longitudinal axis of member 2 for guiding the stems of the hedge or shrub to be trimmed, such as stem 4 depicted in the Figure. A cooperating elongated member designated 5 in the figure includes a plurality of individual blades 6 disposed generally perpendicular to the longitudinal axis of blade carrying member 5 and arranged to alternately cover and uncover the slots 3 upon reciprocation of the blade carrying member 5 in the direction shown by the arrows in FIG. 1. Stem guiding member 2 is generally fixed to a frame in housing 7 which also contains the mechanism (not shown) for reciprocating blade carrying member 5. Frame 7 can also contain a rechargeable battery pack (not shown) for self-contained units. FIG. 1 also shows the successive positions of an individual blade, blade 8a, during one-half cycle of reciprocation, showing the movement of the blade completely across the corresponding stem-guiding slot, as is conventional. It is also known to size the overall lengths of the stem-guiding member 2 and the blade carrying member 5 in accordance with the power capacity of the apparatus.
In conventional trimming apparatus of the type described above, stems which have been guided into the slots by the action of the operator have a tendency to move in a counter direction, that is, in a direction out of the slot upon engagement by the blade member. This tendency is particularly pronounced when the individual blade members are generally trapezoidal in shape, as blade 6 shown in FIG. 1, wherein the resultant force on the stem has a component along the axis of the slot. If the frictional engagement between the stem and the slot and the stem and the blade is insufficient, the stem will tend to move out of the slot and be only partially severed by the action of the blade, or escape cutting entirely. This problem can become particularly acute after periods of prolonged use of the trimming apparatus after the blades have become worn and a greater cutting force is required to sever the stem.
Attempts have been made to control the movement of stems, including the use of blades having recessed, curve-shaped cutting edges. However, production costs for such intricate blade shapes can be prohibitively high, and any sharp corner projections on the moving blades will have a tendency to "spear" and mangle the stems rather than cut them cleanly.
FIG. 2 shows another prior art attempt to control stem movement. In the FIG. 2 apparatus, the edges defining the individual stem guide slots are equipped with barb-like projections 9 located at approximately the outermost position of the tips of the cutting blades. These barbs have not been entirely successful in preventing the escape of stems from the slots when acted upon by the blades. The stems still can move in the direction out of the slots such that only the portion of the stem inboard of the barbs 9 is actually severed upon passage of the blade. Therefore, the partially cut stems must be acted upon by several passes of an individual blade before being completely severed. As a result, the severed stems typically have a mangled and shredded appearance, and this type of cutting operation is generally unacceptable. Furthermore, while this type of cutting operation might be tolerated when an unlimited power supply is present, the finite power capacity of the self-contained, rechargeable battery operated trimmers requires a more efficient cutting operation.
Specifically, inefficiencies in the cutting operation with conventional trimming apparatus can result in unreasonably short times between recharging and/or the need for larger, heavier power packs. Either condition can make the trimming device commercially unattractive.